1. Field of the Invention
The present invention relates to, in general, a toothbrush with tapered bristles and a method of manufacturing such toothbrushes, in particular, to a toothbrush with highly tapered bristles having high flexibility and a method of manufacturing the same.
2. Description of the Prior Art
A conventional monofilament for bristles of toothbrushes is made of nylon. The nylon monofilament bristles have the advantages of proper resilience and flexibility, but are disadvantageous in that they are highly water-absorbent and are easily deformed. The nylon monofilament bristles are not soft because they must be thick in order to maintain desired flexibility. Generally, the nylon monofilament bristles are each rounded at their ends in order to prevent the gums from being injured during brushing, as shown in FIG. 1.
Polyester compounds such as polybutylene terephthalate or polyethylene terephthalate, may be used as material for the monofilament bristles of toothbrushes. In comparison with nylon bristles, the polyester compound bristles have advantages of a lower price, good durability, and lower water-absorptivity, and so such polyester compounds are preferable for bristles of toothbrushes. However, the monofilament bristles made of such polyester compounds are too stiff and inferior in their flexibility, and may damage or injure the gums. The polyester compounds have been typically used as the materials for bristles of inexpensive disposable toothbrushes, or the polyester compound bristles used in combination with nylon bristles, as a way to reduce the cost.
To avoid the above disadvantages, there was proposed a process of tapering the ends of such polyester compound bristles into a needle-shape. Conventionally, such tapering of the bristles was done mechanically by the blade of a knife or an abrader, as shown in FIG. 2. But, it is almost impossible to overcome the above disadvantages of the polyester compound bristles by such mechanically and slightly tapering the ends of the bristles.
Many studies have been made to avoid such disadvantages. For example, reference may be made to a patent owned by the inventor of the present invention, Korean Patent No. 130932 (hereafter, refer to xe2x80x98first prior artxe2x80x99), which discloses a method of tapering a monofilament for bristles using chemicals. The method disclosed in the Korean Patent comprises the steps of (i) cutting a monofilament made of polybutylene terephthalate or polyethylene terephthalate in such a way that the length of a primarily cut monofilament is longer than a target length by 1 to 4 mm, (ii) vertically dipping the surplus portion of the primarily cut monofilament into a sulfuric acid in order to remove the surplus portion of the primarily cut monofilament, in addition to tapering the end of the monofilament to form the target length of a resulting filament.
According to the first prior art, highly tapered bristles are obtained, each of which is tapered starting at a position of 4 to 10 mm from an end of the bristle, with the free end of the bristle being 0.01 mm in diameter, as shown in FIG. 3.
The first prior art provides bristles with a somewhat desired softness by reducing the stiffness of the polyester compound filaments such as polybutylene terephthalate filaments, and easily removing an odontolith from a periodontal pocket by highly tapering the end of the monofilament, as shown in FIG. 3.
However, the first prior art exhibited the following problems:
1) A toothbrush with bristles made by the method of the first prior art felt too soft by some users familiar with conventional toothbrushes with nylon bristles. Such users thus determine the brushing effect of the toothbrushes to be not desirable.
2) Since the highly tapered bristles are manufactured using chemicals, the tapering process is too difficult as the processing conditions such as a concentration of chemicals, a temperature, and the duration of dipping are difficult to precisely control. Therefore, the ends of the highly tapered bristles are not uniform. As a result, defective products are produced in 50% or more of the time.
To avoid these problems, another reference may be made to a patent owned by the inventor of the present invention, Korean Patent No. 261658 (hereafter, referred to as the xe2x80x98second prior artxe2x80x99), which discloses a method of tapering a monofilament for the bristles of toothbrushes. This method comprises the steps of (i) primarily cutting a filament made of polybutylene terephthalate or polyethylene terephthalate into bristles having a target length, (ii) dipping the bristles into a strong alkali or acid solution at the temperature of 100 to 180xc2x0 C. until the bristles shorten, (iii) rinsing the bristles with water, (iv) drying the bristles, (v) attaching the bristles on the head of a toothbrush, (vi) cutting the free ends of the bristles of the toothbrush to 0.5 to 1.5 mm, and (vii) grinding the ends of the bristles until the ends are 0.04 to 0.08 mm in diameter. A cross sectional view of a tapered bristle according to the second prior art is illustrated in FIG. 4.
Overcoming the low flexibility of the bristles according to the first prior art, the bristles of the second prior art, however, suffer from disadvantages in that it is difficult to remove the odontolith from a periodontal pocket because the diameter of the bristle ends in the second prior art, which ranges from 0.04 to 0.08 mm, is undesirably larger than that of the bristles in the first prior art, and the price of the bristles according to the second prior art is cheaper in that it is 25% of the price of the bristles in the first prior art.
It is therefore an object of the invention to avoid the disadvantages of the prior arts, and provide highly tapered bristles with appropriate flexibility suitable for preventing injury to the gums and removing an odontolith from a periodontal pocket.
It is another object of the present invention to manufacture such highly tapered bristles without wasting bristle material.
It is still another object of the present invention to provide highly tapered bristles which are comfortable to a user while toothbrushing.